1. Field of the Invention
The present invention relates to an optical disk apparatus for optically recording on the optical recording medium or reproducing the recorded information therefrom and, more particularly, to an optical disk apparatus for optically recording and reproducing an information from an optical disk.
2. Description of the Prior Art
One effective means of improving the recording density of an optical disk apparatus is to reduce the track pitch. Unfortunately, cross talk of the signals reproduced from adjacent tracks to a target track increases when the track pitch is reduced. A method for solving such problem, for example, which the Japanese Laid-open Patent Publication No. 57-58248, published Apr. 7, 1982 proposes is described with reference to FIG. 25. When a target signal SC is reproduced from a target track 2C by a laser spot 1C impinged thereon, the edge of the laser spot 1C intrudes into the range of the adjacent tracks 2L and 2R. As a result, three signals are simultaneously reproduced from three tracks 2L, 2C, and 2R laser spot 1C representing different information recorded on tracks 2L, 2C, and 2R, respectively. Thus, the target signal SC from the target track 2C is interfered by the noise signals from the adjacent tracks 2L and 2R, suffering from a cross talk caused by those signals.
To eliminate this problem, additional laser spots 1L and 1R are provided to scan the adjacent tracks 2L and 2R. The signals from the adjacent tracks 2L and 2R are therefore simultaneously played back, multiplied by a given constant, and subtracted from the intended track 2C signal to reduce crosstalk interference from the adjacent tracks 2L and 2R. The resulting signal S can be defined by the equation of EQU S=SC-K.times.(SL+SR)
where SC is the reproduced signal from track 2C output by the first laser spot 1C, SL and SR are the playback signals from tracks 2L and 2R output by laser spots 1L and 1R, respectively, and K is a constant.
However, as will be obvious, the method of the prior art as thus described requires three laser spots to simultaneously read the signals from the target track and the two tracks adjacent thereto. This results in a more complex optical system, and makes it difficult to reduce unit size and cost, and to improve reliability.